The present invention relates to a device for simulating with great precision and for a wide range of applications, the thermal state of an object which is the seat of energy dissipation.
This device is particularly interesting in all the cases where the direct measurement of the temperature of the object is not possible because of its physical characteristics or because of the speed of change of this temperature.
This device for measuring the temperature of a given point of an object finds more particularly interesting applications in the thermal protection of semi conductor devices such as static relays or electronic power controllers (EPC) which may have high dissipation under stable or transitory operating conditions.
It is in fact known that temperature measurements are difficult to make particularly in the cases where:
the temperature probe disturbs the thermal state of the object to be measured.
the object to be measured is physically inaccessible.
the distance between the point to be measured and the thermometer introduces errors and delays, this being particularly true for the measurements of the temperature of semiconductor junctions where it is impossible to implant a thermometer at the level of the junction itself.
the means to be used are unsuitable for many applications.
A first improvement of these temperature measurements is obtained by the simultaneous use:
of a conventional temperature probe situated at a given distance from the point whose temperature it is desired to measure.
of a model representative of the temperature differences between the temperature probe and the point at which the temperature is to be measured.
of information concerning the powers dissipated in the device to be protected, which information is very often obtained readily by electric current and/or voltage measurements.
The principle of such a device for simulating the thermal state of an object has already been described by the inventors in a communication related to a thermal transmission model and presented during the fourt ESTEC Seminar (Spacecraft Power Conditioning Seminar) which took place in September 1982 at Noordwijk (Netherlands).
Since the discovery of this model, new and very important improvements hae been made to this device making it usable in practice with very good performances in all possible conditions of use.
Thus the present invention relates to a temperature measuring, protection and safety device using a model of the thermal transmission between the object or point to be protected and the point where the temperature is measured, comprising an initialization device for, at the time of switching on or of switching on again, positioning the sate of the thermal model at an operating point representative of the real temperature of the object to be protected, initialization being effected by preloading in a very short time a series of capacitors up to a potential representative of the measured temperature.
The present invention also relates to a thermal protection device for a "solid-state" electronic circuit, using the measuring device of the invention, with an analog network representative of a thermal model of the circuit to be protected, means being provided for isolating the analog network and thus allowing it to be representative of the thermal state of the circuit to be protected, whatever the electric state of the upstream circuits and of the circuits internal to said device.
The present invention relates furthermore to an electronic power controller, including a thermal protection device of the invention and further comprising several electronic "solid state" circuits with their individual control circuits, said "solid state" electronic circuits being connected in parallel.